The invention relates to a cell coil for a lithium-ion accumulator having at least two sub-cells which are wound in a space-saving fashion and thermally coupled to one another.
It is apparent that in future new battery systems or accumulator systems which will have to fulfill very stringent requirements in terms of reliability, safety, efficiency and service life will be used in stationary applications, for example in wind turbines, in motor vehicles which are configured as hybrid vehicles or electric vehicles as well as in electrical appliances.
Owing to their high energy density, in particular lithium-ion accumulators are used as energy stores for electrically driven motor vehicles.
DE 10 2011 017 613 A1 discloses a cell coil for a lithium-ion accumulator. The cell coil comprises two current conductors which are wound to form the cell coil with the intermediate positioning of two separators.
DE 10 2011 110 876 A1 discloses an energy storage device. The energy storage device comprises, inter alia, an energy storage cell, for example in the form of an electrode coil, and a container for holding the energy storage cell. So that the function of the energy storage cell can be reliably ensured, a thermally conductive layer, by which heat can be carried away from the energy storage cell in the direction of the container wall, is provided between the electrode coil and the container wall. In one preferred configuration there is provision that the thermally conductive layer has a partial layer composed of an electrically insulating material. The partial layer ensures, on the one hand, that released heat can flow away satisfactorily from the cell, and on the other hand the partial layer prevents an outer side of the cell from coming into electrical contact with the container wall. Furthermore, the partial layer ensures that in the case of punctiform penetration by a foreign body from the outside short-circuits between the individual electrodes are avoided.
It is disadvantageous, inter alia, that in the case of a fault, in particular in the case of an internal short-circuit of a cell or the like, the energy storage cell does not have any individual cells which can be switched off selectively in order to limit damage.
The probability of the occurrence of internal short-circuits in lithium-ion accumulators can be reduced e.g. by enhanced quality measures during production. However, in this context, all faults cannot be detected and eliminated continuously at an acceptable level of expenditure. Moreover, it is possible to make lithium-ion accumulators mechanically more robust, with the result that external effects, in particular mechanical and thermal effects cannot so easily cause an internal short-circuit. The relatively large material thicknesses which are generally necessary for this purpose and the additional mechanical protective components also have the effect of increasing costs and additionally reduce the volume portion and weight portion of the overall weight which is made up by the active material, and in association with this the electrical energy density of the accumulator. Furthermore, the tendency of lithium-ion accumulators to short circuit can be positively influenced by the selection of other active materials for the electrocoating and/or the use of less active material on the electrodes. However, in this case a reduction in the available capacity of the lithium-ion accumulator also occurs.